Modular tap-changing selector switch for connecting selectively fixed tap contacts to a transfer switch



July 13, 1965 BLEIBTREU 3,194,900

MODULAR TAPCHANGING SELECTOR SWITCH FOR CONNECTING SELECTIVELY FIXED TAP CONTACTS To A TRANSFER SWITCH Filed Dec. 15, 1962 5 Sheets-Sheet 1 2 za-l fel l 23 /NVENR9P (Wm/am W M "MN/M A. BLEIBTREU July 13, 1965 MODULAR TAP-CHANGING SELECTOR SWITCH FOR CONNECTING SELECTIVELY FIXED TAP CONTACTS TO A TRANSFER SWITCH Filed D80. 13, 1962 3 Sheets-Sheet 2 I I a Ml-ling! lNVEA/IUP (Wm/AM WA WM July 13, 1965 A. BLEIBTREU 3,194,

MODULAR TAP-CHANGING SELECTOR SWITCH FOR CONNECTING SELECTIVELY FIXED TAP CONTACTS TO A TRANSFER SWITCH Filed Dec. 15, 1962 5 Sheets-Sheet 5 Z. ,4 7 x5 #2 x9 2 I II I 2 X; 7 I

f0 6 426 a E g 7 f3 8 U Alva-wrap UMM Wm M MW W y United States Patent 3,194,900 MQDULAR TAP-CHANGING SELECTGR SWITCH FQR CONNECTHNG SELECTTVELY FIXED TAP QGNTACTS TO A TRANSFER SWITCH Alexander Elcihtreu, Regenshur Germany, sis-signer to Masehinenfahrik Reinhausen Gebriider Scheuheclr K.G., Regenshnrg, Germany iled Dec. 13, 1962, Ser. No. 246,289 Claims priority, application Germany, Dec. 20, 1961, M 51,244 Claims. (CL, 206-11) This invention has reference to load tap changers for regulating transformers and more particularly to selector switches for load tap changers.

It is a general object of this invention to provide improved load tap changers for regulating transformers, both single phase and polyphase'regulating transformers, and to provide improved selector switches for such load tap changers.

A further object of this invention is to provide load tap changers for transformers having a relatively large number of taps and selector switches for such load tap changers, which load tapchangers and selector switches are considerably more compact, and involve considerably smaller manufacturing cost, than comparable prior art load tap changers and selector switches.

Load tap changers include selector switches and transfer switches. The selector switches serve the purpose of selecting a particular tap on a tapped transformer winding intended to be connected into an electric circuit. Selector switches are not required to interrupt or close on current-carrying circuits. This task is performed by the transfer switches. The latter perform all switching operations under load. Therefore all arcing is restricted to the transfer switches, the selector switches merely selecting the particular transformer tap to which the load is to be transferred.

Polyphase transformers require a selector switch and a cooperating transfer switch for each phase of the circuit.

in the method of tap changing a current-limiting device must be employed during each transition period from one tap position to the other. Such current-limiting devices may either be reactors or resistors. This invention is particularly concerned with load tap changers wherein resistors are used as current limiting devices.

Load tap changers utilizing resistors as currentdimiting devices and fast operating transfer switches are known, or referred to, as Jansen type load tap changers. This type of load tap changers has important advantages over load tap changers of other kinds. In this type of load tape changers the current-limiting resistors are in parallel with respect to the load current and in series with respect to the circulating currents which flow during transition times between tap changes. This makes it possible to reduce the resistance of the current-limiting resistors to relatively low ohmic values without giving rise to large circulating currents. In Jansen type tap changers the movable contacts of the transfer switches move at high speeds, or with a snap action, wiping over the fixed contacts to which the current-limiting resistors are connected. As a result of this fast motion the transition periods during which the currentlimiting resistors must carry load Patented July 13, 1965 currents are very short, say in the order of a few hundredth of a second. This has two significant advantages: The current-limiting resistors can be made very small and the voltage fluctuation resulting from tap changes insignificant. The rapid operation of the transfer switches is produced by stored energy means, preferably wound up springs which are maintained in a pie-wound, or preloaded, condition in readiness for the next tap-changing operation. Load tap changers of the Jansen type are well known in the art and have been described in many printed publications such as, for instance, the book by H. P. Young, Electric Fewer Systems, London, England, Chapman 8; Hall Ltd. 1942 and reference may be had to such publications for a more complete description or" Jansen type load tap changers, and the structural features and operating characteristics thereof.

It is another object of this invention to provide improved lansen type load tap changers for single phase and/ or polyphase transformers.

Selector switches for tap-changing regulating transformers require diiferent'parts, depending upon the particular tap-changing transformer under consideration. This tends to greatly increase the cost of designing and of manufacturing such selector switches.

It is, therefore, one of the principal objects of this invention to provide selector switches for tap-changing regulating transformers which are of modular design and include basic parts which are adaptable to many applications.

Anot er object of this invention is to provide modular relatively compact and simple selector switches for load tap changers having a relatively large number of operating positions subdividing the entire regulating range into a large number of portions.

The foregoing and other general and special objects of the inventionand advantages thereof will appear more clearly from the ensuing particular description of the invention as illustrated in the accompanying drawings showing diagrammatically the parts associated with one phase of a polyphase tap-changing regulating transformer including a selector switch embodying the invention.

in the drawings:

HG. 1 is a diagrammatic representation of one phase of a tapped polyphase transformer including a selector switch and a transfer switch, the former switch embodying the present invention and being illustrated isometrically in FIG. 1;

FIG. 2 is an isometric representation of the selector switch included in FIGURE 1, FIGURE 2 diflering from FIGURE 1 in that the constituent parts of the selector switch are shown in their actual shapes rather than but diagrammatically indicated therein;

H6. 3 is a vertical section of the selector switch shown in FIG. 2; and

FIG. 4 is a section along lVlV of FIG. 3.

Referring now to PK}. 1, reference character Tr has been applied to generally indicate a tapped winding of phase U of a three phase transformer, reference character S has been applied to generally indicate a composite selector switch cooperatively related to phase winding Tr, and reference character 22 has been applied to generally indicate a, transfer switch cooperatively related to selector switch S.

ans teen The general arrangement of parts in, and the operative interrelation of parts of, Jansen type load tap changers such as that shown in the present drawings have been disclosed in considerable detail in the copending patent application of Alexander Bleibtreu et al., Ser. No. 204,929, filed June 1962 for Load Tap Changer for Transformers, and reference may be had to that application for certain details and aspects of Jansen type load tap changers which may be of general interest in connection with the present invention, but are not immediately relevant to the present invention.

As shown in FIG. 1 of the drawings the transformer phase winding Tr is provided with a relatively large number of spaced taps. To be more specific, winding Tr is provided with sixteen taps which have been numbered consecutively ii, 2, 3, 4 15, 16. The selector switch S comprises a number of tubular units of insulating material or casting resin which are stacked or arranged to form a vertical column 1. Selector switch S comprises sixteen fixed contacts 3, consecutively numbered 1, 2, 3 i t, 15, 16, a pair of fixed annular contact structures 6, 7 and a pair of rotatable movable contacts or contact arms 2 adapted to sequentially engage the aforementioned fixed contacts 3, numbered 1, 2, 3 14, 15, To. Each tap of tapped transformer winding Tr is conductively connected to the fixed selector switch contact 3 bearing the same reference numeral as the particular tap. Thus tap it of winding Tr is conductively connected to fixed contact numbered I of selector switch S and tap 16 of winding Tr is conductively connected to fixed contact numbered 16 of selector switch S. For reasons of clarity the wiring between the taps and the fixed selector switch contacts has only been shown in part in FIG. 1 of the drawings. The

fixed contacts numbered ll, 2, 3 i4, 15, 16 of selector switch S are arranged in two parallel spaced planes, even numbered contacts 2, 4 14, 1e being arrangedin a lower plane and odd numbered contacts 1, 3 T3, 15 in a higher plane. The upper contact arm 2 pivota'ble about the vertical axis of column 1 around column 1 is adapted to establish conductive connections between the upper ring contact 6, 7 and any of the upper level fixed contacts numbered 1, 3 13, 15. The lower contact arm 2 pivotable about the vertical axis of column 1 around column 1 is adapted to establish conductive connections between the lower ring contact 6, 7 and any of the lower level fixed contacts numbered 2, 4 14, 16. As will be shown below more in detail, the hollow interior of column 1 accommodates a pair of conductors 17 extending in a direction longitudinally of column 1. The upper ends of conductors 17 are conductively connected to ring contacts 6, '7 while their lower ends are conductively connected to transfer switch 22. Transfer switch 22 comprises a first pair of movable contacts 23 and a second pair of movable contacts 24. Both pairs of contacts 23, 24 are gang operated and, therefore, all contacts 23, 24 are moved simultaneously to their two limit positions, FIG. 1 showing the right limit position of contacts 23, 24. Contacts 24 are adapted to cooperate with fixed contacts con trolling the current paths through change-over resistors 25. The lower set of fixed contacts cooperating with movable contacts 23, 24 are conductively interconnected. The winding Tr forms part of a polyphase transformer which is Y connected and the lower set of fixed contacts coopcrating with movable contacts 23, 24 is conductively connected to the neutral point of the Y connection of the three transformer windings of which but one has been shown in FIG. 1. This has been indicated in FIG. 1 by adding the Y symbol below transfer switch 22.

In the right limit position of transfer switch 22 shown in FIG. 1 only the right movable contact 23 is in engage ment with its cooperating fixed contacts; all other movable contacts 23, 24, are out of engagement with their cooperating fixed contacts.

In the position of the parts of the selector switch which is shown in FIG. 1 the upper movable contact arm 2 establishes a conductive connection between fixed contact numbered 11 connected to tap 11 of winding Tr and upper annular contact 6, '7; and the lower contact arm 2 establishes a conductive connection between fixed contact 12 connected to tap T2 of winding Tr and lower annular contact 6, 7. This establishes the following circuit: Tap 12 of winding Tr, fixed contact 12, lower annular contact 6, 7, right lead 17, right movable contact 23 of transfer switch 22, neutral point of the Y-connected phase windings.

The fact that the upper level contact arm 2 establishes a conductive connection between fixed contact 11 and the upper level annular contact 6, 7 means that tap if has been pre-selected and that, upon moving of the gang operated contacts 23, 24 of transfer switch 22 from their right limit position shown in FIG. 1 to their left limit position, tap 11 of winding Tr will be connected to neutral rather than tap In the left limit position of transfer switch 22 the left movable contact 23 thereof is in engagement with its cooperating feted contacts and the right movable contact 23 thereof is out of engagement with its cooperating fixed contacts. During the motion of transfer switch 2?. from the right limit position thereof to the left limit position thereof the movabie contacts 24 engage temporarily their cooperating fixed contacts and by so doing insert temporarily resistors 25 into the circuit of winding Tr. In the left limit position of transfer switch 23 the latter establishes the following circuit: Tap ll of transformer winding Tr, fixed contact numbered 11 of selector switch S, contact arm 2 on the upper level of selector switch S, annular contact structure 6, 7 on the upper level of selector switch S, left conductor 17, left movable con tact 23 of transfer switch 22-, neutral point of the Y-connected phase windings.

it appears from the foregoing that each position of selector switch S prepares one tap of winding Tr to be subsec uently inserted into the circuit, in addition to actually inserting another tap of winding Tr into the circuit. Transfer switch 2.2 moves between its limit positions each time another tap is being inserted into the circuit. Transfer switch 22 may be operated by means of a Geneva gear drive, as commonly used in the art for operating transfer switches. The movable contact arms or contacts 2 are coupled by appropriate tie means (not shown) for joint motion. Their joint motion may be in clockwise direction or in counterclockwise direction, depending upon whether it is intended to step down or to step up the voltage in phase U of the circuit.

In FIG. 1 transfer switch 22 has been illustrated but diagrammatically since it does not form a part of the present invention. Transfer switch 22 may be designed in the fashion more fully set forth in United States Patent 2,680,- 790 to B. Jansen, Load Changeover Switch for Tapped Transformers Using a Combination of Contact Movements, June 8, 1954, or in the aforementioned copending patent application Ser. No. 204,029.

Referring now to FTGS. 2-3, inclusive, numeral 1 has been applied to generally indicate a hollow insulating column made up of a plurality of relatively short tubular bodies of casting resin which are superimposed in coaxial relation. As shown in the drawing (see particularly FIG. 3) the number of superimposed tubular bodies of casting resin is three, i.e. column 1 includes the axially outer or upper and lower tubular bodies 5 of casting resin and the intermediate tubular body 4 of casting resin. Bodies 4- and 5 may be made of casting resins which are known in the trade as Epoxy casting resins. Tubular bodies 5, 4, 5 form two contiguous pairs, is. the pair 5, 4 comprising upper body 5 and intermediate body 4 and the pair 4, 5 comprising the intermediate body 4 and the lower body 5. Bodies 4, 5 are provided with fixed annular contacts or ring contacts adjacent juxtaposed end surface thereof. There is, therefore, a pair of fixed ring contacts at each point where a pair of tubular bodies 5, 4, 5 faces each other. Reference numeral 6 has been applied to indicate one of these pairs of fixed ring contacts, namely the ring contact of each pair arranged at the higher level and reference numeral 7 has been applied to indicate the other of these pairs of fixed ring contacts, namely the ring contact of each pair arranged at the lower level. Each ring contact 6,7 is rectangular in crosssection and comprises two flange portions. The radially inner or vertical flange portion 3 of each ring contact is, 7 is arranged within resin castings 5, 4, 5 thus integrating ring contacts a, 7 and castings 5, 4, 5 into self-sustained structural units. The radially outer or horizontal flange portion 9 of each ring contact 6, 7 is exposed, projecting radially outward from the radially outer lateral surfaces of tubular resin castings 5, 4, 5. As clearly shown in FIG. 3 pairs of radially outer or horizontal flange portions 9 of immediately adjacent pairs of ring contacts a, 7 are arranged in abutting relation, thus forming electrically rather than merely mechanically one single integral contact. A movable contact 2 is adapted to cooperatively engage each composite ring contact 6, 7. Movable contacts 2 are adapted to be pivoted about the longitudinal axis of column ll around column 1. While being so moved each movable contact 2 slidably engages a pair of exposed radially outer or horizontal flange portions of a pair of immediately adjacent ring contacts 6, '7. Screw means 13 project transversely through abutting pairs of radially outer flange portions '9 of immediately adjacent pairs of ring contacts a, 7, thus establishing a firm mechanical tie between resin castings 5, 4 and resin castings 4, 5. Ring contacts 6, 7, i.c. radially oute or horizontal flange portions 9 thereof, jointly define an annular groove 1t) accommodating an insulating ring 11 conforming to the shape of groove lit. Groove 1d and ringll are preferably rectangular or square in crosssection. Ring 11 is provided with a projection plate or projection tab 12 forming an integral part thereof extending radially outward from groove it). Each ring 11 is slidably arranged within its groove 1t) and is coupled by projection plate 12 for joint motion with one of the movable contacts or contact arms 2. Each contact or contact arms 2 includes a pair of stacks formed of spaced contact laminations 18 arranged in parallel planes. The spaces between adjacent contact laminations 18 are filled by steel plates 20. A steel plate 26 is further arranged at the ends of each stack of contact laminations 18 (see FIG. 4). The constituent contact laminations 18 of movable contacts 2 are arranged inside of a housing 25 and resiliently supported therein by helical springs 21. The contact laminations 18 by which movable contacts or contact arms 2 are made up engage edgewise slidably opposite surfaces on abutting pairs of flange portions 9 of immediately adjacent fixedcontact rings 6, 7. The ends of contact laminations 18 juxtaposed to ring contacts 6, 7, Le. the radially inner ends of Contact laminations 18 are provided with substantially V-shaped recesses 19 receiving the annular rim formed by a pair of abutting flange portions 9. Springs 21 interposed between housing 25 and contact laminations 18 provide the required amount of contact pressure between contact laminations 18 and flange portions 9. As clearly shown in FIG. 3 the cross-section of flange portions 9 is increased adjacent the point of engagement of the latter by contact laminations 18, the cross-section of the circular rim formed by abutting flange portions 9 being more or less circular or bulbous. The aforementioned radial projection 12 of contact guiding ring 11 projects into the housing 25 for contact laminations 18 and is secured to said housing by screws clearly shown in FIGS. 2 and 4. The three tubular units 5, 4, 5 formed of a casting resin are each provided with an integral outwardly projecting flange 14 located between the upper end surface and the lower end surface of the respective unit. The upper resin casting 5 and the intermediate resin casting 4 each have a recess in the radially inner lateral surface thereof giving ac cess to, or exposing from the inside of these parts, a short length of the radially inner flanges of the upper and lower annular contact 6. The space bounded by tubular casting resin units 5, 4, 5 accommodates the electric conductors 17 extending in a direction longitudinally of that space, or of the column formed by parts 5, 4, 5. Each conductor 17 is contained inside of a sleeve of insulating material. Conductors 17 establish conductive connections between the selector switch of a tapped regulating transformer and the transfer switch thereof, as shown in FIG. 1 and more fully explained in connection with that figure. As clearly shown in FIG. 3 each conductor 17 is provided with a terminal element 26 arranged within the aforementioned recess 15 and conductively connected to the radially inner flange of one of the ring contacts 6. Ring contacts 6 are of increased height at the point where they are engaged by terminal elements 2.6, and this point has been indicated in PEG. 3 by reference numeral 16. The enlarged points 16 of rings 6 are conductively connected to terminal elements 26 by screws 27 projecting through both parts. As stated in connection with PEG. 1 movable contacts or contact arms 2 are intended to establish conductive connections between ring contacts 6, 7 and a plurality of radially outer fixed contacts 3 which have been numbered consecutively 1-16. FIG. 3 shows at the right and at the left thereof one of the aforementioned fixed contacts 3. The steel plates 2?; between which cont-act laininations 18 are arranged provide means for guiding these laminations and for minimizing friction.

It will be understood that the number of intermediate units 4 may be increased wherever necessary or desirable. This will be the case where the number of taps per transformer winding is large, say 32 instead of but 16, as

shown in the above described embodiment of the I invention. 7

it will be apparent that any selector switch for any kind of tap changer for regulating transformers can readily be assembled with the three modular elements shown and described above in detail.

It will be understood that I have illustratcd and described herein a preferred embodiment of my invention, and that various alterations may be made in the details thereof Without departing from the spirit of the invention as defined in the appended claims.

I claim as my invention:

1. A modular tap-changing selector switch for connecting selectively fixed tap contacts to a transfer switch, said selector switch comprising:

(a) a plurality of relatively short tubular insulating bodies of a casting resin superimposed in coaxial abutting relation to form a composite hoilow insulating column;

(b) a plurality of contact bridges arranged at different levelsand mounted for pivotal motion about the axis of said column, each of said plurality of contact bridges having a radially inner contact end and a radially outer contact end; and

(c) a plurality of fixed ring contacts arranged in co axial relation to and supported by said column, each of said plurality of ring contacts being arranged at a different level at a point of abutting engagement between contiguous pairs of said plurality of insulating bodies and each of said plurality of ring contacts comprising a pair of complementary parts having a pair of radially inner endseach integral with one of said plurality of tubular insulating bodies, each of said pair of complementary parts further having a pair of radially outer ends in sliding engagement with said radially inner contact end of one of said plurality of contact bridges, and said pair of complementary parts further having a pair of intermediate portions being arranged in abutting relation.

2. A modular tap-changing selector switch for connecting selectively fixed tap contacts to a transfer switch, said selector switch comprising:

(a) a plurality of relatively short tubular bodies of casting resin superimposed in coaxial relation to form a hollow insulating column;

(b) a plurality of ring contacts supported by said plurality of tubular bodies, said plurality of ring contacts being arranged in pairs adjacent juxtaposed end surfaces of contiguous pairs of said plurality of tubular bodies, each of said plurality of ring contacts being substantially angular in cross-section and including a radially inner flange portion arranged within one of said plurality of tubular bodies and each of said plurality of ring contacts further including a radially outer exposed flange portion projecting radially outward from the radially outer lat eral surface of one of said plurality of tubular bodies, pairs of radially outer flange portions of immediately adjacent pairs of ring contacts being arranged in abutting relation; and

(c) a plurality of movable contacts mounted for pivotal motion about the axis of said column around said column each slidably engaging a pair of radially outer flange portions of a pair of immediately adjacent abutting ring contacts.

3. A selector switch as specified in claim 2 comprising screw means projecting transversely through abutting pairs of radially outer flange portions of immediately adjacent pairs of ring contacts and establishing mechanical ties between contiguous pairs of said plurality of tubular bodies.

4. A modular tap-changing selector switch for connecting selectively fixed tap contacts to a transfer switch, said selector switch comprising:

(a) a plurality of relatively short tubular bodies of casting resin superimposed in coaxial relation to form a hollow insulating column;

(b) a plurality of ring contacts supported by said plurality of tubular bodies, said plurality of ring contacts being arranged in pairs adjacent juxtaposed end surfaces of contiguous pairs of said plurality of tubular bodies, each of said plurality of ring contacts being substantially angular in cross-section and including a radially inner flange portion arranged within one of said plurality of tubular bodies and each of said plurality of ring contacts further including a radially outer exposed flange portion projecting radially outward from the radially outer lateral surface of one of said plurality of tubular bodies, pairs of radially outer flange portions of immediately adjacent pairs of ring contacts being arranged in abutting relation;

(c) a plurality of movable contacts mounted for pivotal motion about the axis of said column around said column each slidably engaging a pair of radially outer flange portions of a pair of immediately adjacent abutting ring contacts;

(d) a plurality of insulating rings each inserted with the radially inner side thereof into the open radially outer side of an annular groove defined by one of said plurality of ring contacts, the radially inner side of each of said plurality of insulating rings conforming to the shape of and being guided by said groove, and each of said plurality of insulating rings having a projection extending radially outward from said groove; and

(e) means for coupling for joint movement each of said plurality of movable contacts with said projection on one of said plurality of insulating rings.

5. A selector switch as specified in claim 2 wherein each of said plurality of movable contacts includes a pair of stacks formed of spaced contact laminations resiliently supported in a common housing, the constituent laminations of said pair of stacks engaging edgewise slidably opposite surfaces on abutting pairs of ring contacts adjacent juxtaposed end surfaces of contiguous pairs of said plurality of tubular bodies.

6. A selector switch as specified in claim 2 wherein the radially outer ends of abutting pairs of radially outer flange portions of ring contacts are substantially semicircular in cross-section, said radially outer ends jointly forming an annular rim, and wherein each of said plurality of movable contacts comprises a pair of stacks formed of spaced contact laminations, the constituent laminations of one of said pair of stacks edgewise slidably engaging under pressure the upper surface of said rim and the constituent laminations of the other of said pair of stacks slidably engaging under pressure the lower surface of said rim.

7. A modular tap-changing selector switch for connecting selectively fixed tap contacts to a transfer switch. said selector switch comprising:

(a) a plurality of relatively short tubular bodies of casting resin superimposed in coaxial relation to form a hollow insulating column;

(b) a plurality of ring contacts supported by said plurality of tubular bodies, said plurality of ring contacts being arranged in pairs adjacent juxtaposed end surfaces of contiguous pairs of said plurality of tubular bodies, each of said plurality of ring contacts being substantially angular in cross-section and including a radially inner flange portion arranged within one of said plurality of tubular bodies and each of said plurality of ring contacts further including a radially outer exposed flange portion projecting radially outward from the radially outer lateral surface of one of said plurality of tubular bodies, pairs of radially outer flange portions of immediately adjacent pairs of ring contacts being arranged in abutting relation;

(c) a plurality of movable contacts each including a pair of stacks formed of interleaving contact laminations and steel plates, the contact laminations of said pair of stacks edgewise slidably engaging under pressure opposite surfaces or abutting pairs of radially outer flange portions of immediately adjacent pairs of ring contacts; and

(d) a plurality of guide rings each for one of said plurality of movable contacts, each of said plurality of guide rings being arranged coaxially to and centered by said column and slidably supported by one of said plurality of tubular bodies thereof.

8. A modular structure for selector switches for tap changing regulating transformers comprising in combination:

(a) a tubular insulating body of casting resin;

(b) a pair of fixed annular contact means arranged in coaxial relation to said body one adjacent the upper end surface and the other adjacent the lower end surface thereof, each of said pair of fixed contact means having a radially inner flange portion embedded in said body and a radially outer exposed flange portion; and

(c) a pair of movable contact means mounted for pivotal motion about the axis of said body around said body and slidably engaging under pressure the exposed flange portions of said pair of fixed annular contact means.

9. A modular structure for selector switches for tapchanging regulating transformers comprising in combination:

(a) a tubular insulating body;

(b) a pair of fixed annular contact means arranged in coaxial relation to said insulating body one adjacent the upper end surface and the other adjacent the lower end surface thereof, each of said pair of fixed annular contact means being substantially rectangular in cross-section and comprising a radially inner flange portion and a radially outer flange portion projecting radially outwardly from the radially outer lateral surface of said insulating body;

(c) a pair of movable contacts each slidably engaging under pressure said radially outer flange portion of References Qited by the Examiner each of said pair of fixed contact means; and UNETED STATES PATENTS (d) a pair of guide rings each for one of said pair of a movable contacts slidably supported in annular refiiz gg 339-3 cesses defined by said pair of fixed annular contact 5 5 6/49 Hood a1 X means. 2,693,5 73 11/ 54 Perkins.

10(A modular top-changing selector swltch as speci- 3 045 090 7/62 il et 2@ 11 X tied in claim 9 wherein some of said plurality of tubular FOREIC'N PATPNTS insulating bodies have a recess in the radially inner lateral 10 surface thereof exposing a short length of the radially 67779O 7/39 Germany inner side of one of said plurality of ring contacts. BERNARD A. GELHEANY, Primary Examiner. 

1. A MODULAR TAP-CHANGING SELECTOR SWITCH FOR CONNECTING SELECTIVELY FIXED TAP CONTACTS TO A TRANSFER SWITCH, SAID SELECTOR SWITCH COMPRISING: (A) A PLURALITY OF RELATIVELY SHORT TUBULAR INSULATING BODIES OF A CASTING RESIN SUPERIMPOSED IN COAXIAL ABUTTING RELATION TO FORM A COMPOSITE HOLLOW INSULATING COLUMN; (B) A PLURALITY OF CONTACT BRIDGES ARRANGED AT DIFFERENT LEVELS AND MOUNTED FOR PIVOTAL MOTION ABOUT THE AXIS OF SAID COLUMN, EACH OF SAID PLURALITY OF CONTACT BRIDGES HAVING A RADIALLY INNER CONTACT END AND A RADIALLY OUTER CONTACT END; AND (C) A PLURALITY OF FIXED RING CONTACTS ARRANGED IN COAXIAL RELATION TO AND SUPPORTED BY SAID COLUMN, EACH OF SAID PLURALITY OF RING CONTACTS BEING ARRANGED AT A DIFFERENT LEVEL AT A POINT OF ABUTTING ENGAGEMENT BETWEEN CONTIGUOUS PAIRS OF SAID PLURALITY OF INSULATING BODIES AND EACH OF SAID PLURALITY OF RING CONTACTS COMPRISING A PAIR OF COMPLEMENTARY PARTS HAVING A PAIR OF RADIALLY INNER ENDS EACH INTEGRAL WITH ONE OF SAID PLURALITY OF TUBULAR INSULATING BODIES, EACH OF SAID PAIR OF COMPLEMENTARY PARTS FURTHER HAVING A PAIR OF RADIALLY OUTER ENDS IN SLIDING ENGAGEMENT WITH SAID RADIALLY INNER CONTACT END OF ONE OF SAID PLURALITY OF CONTACT BRIDGES, AND SAID PAIR OF COMPLEMENTARY PARTS FURTHER HAVING A PAIR OF INTERMEDIATE PORTIONS BEING ARRANGED IN ABUTTING RELATION. 